1. Field of the Invention
This invention generally relates to testing apparatus for determining the degree to which an object being tested conforms to applicable standards. More particularly, the invention relates to an apparatus for determining the amount of torque required to remove or apply a screw-type closure cap from its associated threaded container.
2. Description of the Prior Art
In the manufacture of packages comprising combinations of screw-type closures with associated containers, it often becomes necessary or desirable to determine the degree to which the threaded or lug-type closure complies with torque specifications. As used herein, the term "threaded closures" also means "lug-type" closures or other "twist-type" closures. For example, the torque with which a threaded closure is applied must be of a certain magnitude in order to properly seal the container so the closure does not become loose during shipment. Additionally, in the packaging of pharmaceutical products, since they can be toxic in the wrong dosages, dosage requirements are somewhat critical and it is often either required or desirable to have a child-proof safety closure limiting access to the container contents. Such safety closures may, for example, comprise a threaded inner cap, for being threaded directly onto the neck of a container, and an overcap loosely rotatable relative to the inner cap. A user must push the overcap axially onto the inner cap to engage a ratchet mechanism to be able to simultaneously turn the inner cap.
During the manufacture of products packaged in containers having threaded closures, the caps may be applied with a capping machine which must be adjusted from time to time to overcome normal mechanical or component variations which may effect application torque. The normal procedure is for periodic quality control checks to be conducted on the packages being produced. During a particular production run, an operator may periodically remove a completed sample product to determine the degree of torque necessary to remove the threaded closure from the associated container. A change of removal torque falling outside an acceptable range indicates the capping machine or other component of the manufacturing process must be adjusted or replaced.
Several prior art devices and methods are known for effecting quality control torque tests of threaded closures to determine the amount of torque required to remove the cap. The standard in the industry is known as the Owens-Illinois Torque Meter which is now manufactured and marketed by Secure Pak, Inc., P.0. Box 14499 Toledo, Ohio 43614. The Owens-Illinois meter is a manual instrument essentially comprising a movable plate, the axis of which is attached via a spring loaded mechanism to a dial or digital meter. The movable plate has four adjustable posts to securely grip the container being tested. The American Society for Testing and Materials (ASTM) has issued an ASTM standard (D-3198-84) which describes the standard test method for determining application and removal torque of threaded or lug-style closures. This standard requires that the container be positioned between the four posts on the torque tester in such a manner that the axis of rotation of the cap is concentric with the center of the movable plate on which the container rests. The closure must then be gripped by hand, avoiding any contact with the container, and the closure must be twisted in the appropriate direction to either apply or remove the closure. The application or removal torque is read off the meter.
While the standard torque meter and test method are simple, there is one disadvantage associated with this prior art. The industry standard method has a built-in bias which is heavily dependent upon operator skill. Given any number of containers being tested, it has been found that any given operator testing for removal (or application or stripping) torque tends to produce a range of values for any particular product. If numerous operators are involved, as may be expected in a manufacturing facility, the torque readings become even more inconsistent and cover a wider range. Additionally, this range is even broader because of several human factors associated with this manual procedure: for example, holding the cap too low so that the operator's thumb touches the container; squeezing the cap too hard thereby making it out-of-round; squeezing too little; twisting with too much velocity or acceleration or little velocity or acceleration, etc. Even when a cap clamp is used, operator-introduced factors still affect the repeatability and consistency of torque values. The inability to obtain consistent readings over a narrow and repeatable range often leads quality control or production personnel to prematurely conclude that the capping mechanism (or other component) needs to be shut down to be either adjusted or repaired when, in fact, if accurate readings were available the manufacturing process could have continued unimpeded for a much longer time period. The unnecessary work stoppage and machine repair is obviously costly and inefficient. Generally, the component most often identified as needing adjustment or rebuilding is the clutch mechanism rotating the cap. It has been found that on production lines using threaded closures the clutch has had to be rebuilt or adjusted relatively frequently (on the order of ten hours or so) because of out-of-tolerance torque tests. Use of this invention has extended the time between clutch rebuilds on the order of 100 hours and more.
In addition to the necessity of using standard torque meters during the manufacturing process, it is also desirable to have a means for simulating the actual torque which a user may apply to a threaded closure when opening a product container. The manner in which a user applies torque to a threaded closure varies gradually from an initial value of zero to some finite value sufficient to open the cap. The normal tendency for a user is to grasp the container in one hand and the cap in the other and twist both in opposite directions. If a significant resistance is encountered, a user would tend to squeeze the cap and container harder while also twisting harder or faster until the cap is unscrewed.
There are known prior art devices which do not rely on the aforementioned manual standard torque meter and attempt to overcome operator-induced errors by using automated equipment. For example, U.S. Pat. No. 4,794,801 (Andrews et al.) discloses a bottle cap removal torque tester utilizing a rotatable motor for rotating a chuck engageable with the cap of a bottle and a torque sensor interposed between the motor and the bottle cap. The container, rotatable chuck, torque sensor and motor are all axially aligned and various other complex mechanical components are disclosed to provide an operable device. Another known device similar to the foregoing is the Auto-torque System manufactured by the Automated Dynamics Corporation, 105 Jordan Road, Renasselaer Tech Park, Troy, N.Y. 12180.
The Andrews et al. patent discloses an apparatus which eliminates the manual rotation of the cap (or cap clamp) and reduces the variation in cap rotational acceleration and velocity in tests conducted by different persons or by the same person at different times. The device provides for electrical rotation of the cap with repeatable control of rotational acceleration and velocity.
One disadvantage of both of the aforementioned devices is that they are costly, complex and, as with any complicated machine, proper operation of each device necessitates a large number of mechanical components operating properly together under satisfactory conditions. Each of these systems has several adjustable variable parameters (e.g. speed, height of chuck over cap, etc.) which could drift during the evaluation period. While such conditions might be found in an enclosed factory quality control area, operation of such devices is generally not suitable on the factory floor where many of the periodic torque checks are made. An additional disadvantage is that these devices are not operable with the industry standard manual torque meter called for in numerous ASTM standards. For example, the use of the industry standard Owens-Illinois Torque Meter is referenced in ASTM standards Nos. D3198-84; D3199-84; D3469-81; D3470-82; D3471-88; D3472-87; D3474-80 (calibration specification); and D3481-86. Use of any different torque sensor is not in compliance with these standards, thereby requiring manufacturers utilizing non-standard, automated torque testers to run duplicate torque tests on the standard (properly calibrated and certified) Owens-Illinois meter.
Furthermore, there already exists a standard procedure for calibrating the Owens-Illinois meter, making its use reliable and conforming to known standards. Procedures have not been standardized for use of any of the known non-standard automated torque testers. Consequently, torque data produced by these testers is most likely to be non-uniform and non-reliable in comparison to industry standards.
It is accordingly an object of this invention to provide an apparatus for determining the removal and/or application torque of a threaded closure on a container, the apparatus enabling the use of an industry standard manual torque meter while simultaneously eliminating many of the operator-induced errors associated with the use of such a manually operated meter.
It is another object of this invention to provide an apparatus for simulating a user's method of opening a threaded closure.
It is yet another object of this invention to provide a torque testing apparatus capable of utilizing the industry standard torque meter in such a way as to eliminate the operator-induced errors generally associated with the standard procedure for utilizing such a torque meter while simulating the manner in which a user may open such a threaded closure.